1. Technical Field
The present invention relates to vehicular collision avoidance and mitigation systems, and more particularly, to a digital map and sensory based collision avoidance system that utilizes data fusion to identify overpasses and modify a threat assessment algorithm, so as to maintain sufficient warning distances, and reduce false alerts.
2. Background Art
A prevailing concern in current implementations of collision avoidance and warning systems in vehicles is that they typically present a significant number of false alerts (i.e. warnings of imminent collisions with objects that are not in fact within the vehicle path). This concern is especially perpetuated by the proximity of stationary objects, the current limitations in accurate prediction of forward path, and the inability of the radar to discriminate between objects present at different elevations. False alerts in conventional systems are often caused by overpasses, mailboxes on the roadside, staled vehicles, etc.
Overpasses are of particular concern for various reasons. First, they are present in great numbers on interstate highways and other thoroughfares. Second, they are typically found traversing the path of thoroughfares having a relatively high speed limit. Third, they are difficult to distinguish from in-path objects that present true potential collisions. Fourth, and perhaps most concerning, current overpass detection algorithms that analyze the signal-strength trend of the approaching object are generally unable to provide sufficient warning distances, when a true potential collision, and not an overpass, is determined.
With respect to the later, once an object is detected at an initial threshold distance, the trend in the radar return signal strength over a plurality of diminishing distances (see, FIGS. 1 through 3a) is assessed to determine the signature signal pattern. Due to the necessity to obtain trend data, however, overpass determination under this and similar methodology often results in the warning being issued at shorter “definite detection” distances, sometimes as short as 60 meters. It is appreciated that a vehicle traveling at the speed of 70 mph (31 meters/sec) requires a warning distance of 150 meters or more in order to allow the vehicle to be stopped before reaching the object (assuming a 1-sec reaction time, and a 0.4 g deceleration).
Thus, to be effective a collision avoidance system must provide reliable and efficient warning distances to the operator, and, therefore, be capable of timely distinguishing false concerns caused by overpasses from potential collisions caused by true in-path objects.